1. Field of the Invention
The present invention relates generally to a viscous fluid type heat generating apparatus generating heat by applying a shearing action to a viscous fluid, and transmitting the heat from the viscous fluid to a heat exchanging fluid flowing through a heat receiving chamber in order to carry the heat to a desired heated area, such as a passenger compartment of a vehicle. Thus, the heat is carried by the heat exchanging fluid to the desired heated area. More particularly, the present invention relates to a viscous fluid type heat generating apparatus provided with a means for ensuring a long operation life of a viscous fluid which is apt to be degraded thermally and physically during the operation of the heat generating apparatus.
2. Description of the Related Art
A viscous fluid type heat generating apparatus intended for use in a vehicle climate controlling system is disclosed in German Laid-Open Patent Publication No. 3832966, i.e., DE-OS-3832966, of which the corresponding U.S. case was issued as U.S. Pat. No. 4,974,778. The viscous fluid type heat generating apparatus of DE-OS '966 and U.S. Pat. No. '778 has a housing in which a heat generating chamber and a heat receiving chamber, working as a water jacket and arranged adjacent to the heat generating chamber to pass a heat exchanging fluid therethrough, are formed. A drive shaft is supported to rotate via bearing devices and shaft seating devices in the housing, and a pulley element is fixedly mounted on a front end part of the drive shaft to be rotationally driven through a belt by a vehicle engine. A rotor element is formed integrally with a rear end part of the drive shaft to be able to rotate in the heat generating chamber. A viscous fluid, such as silicone oil, is filled in a gap between the wall surface of the heat generating chamber and the outer surface of the rotor element. The rotor element generates heat in the viscous fluid when rotated. The heat generating chamber has a storing region communicating with the gap by means of a withdrawing passage and a supply passage. The storing region of the heat generating chamber is provided for storing a given part of the viscous fluid in order to prevent exertion of the shearing action of the rotor element on the stored viscous fluid. The withdrawing passage is formed so as to permit the viscous fluid to positively move from the heat generating chamber into the storing region during the rotation of the rotor element, and the supply passage can be opened and closed by a valve means including a bimetal strip to supply the viscous fluid from the storing region to the gap of the heat generating chamber when it opens.
In the described viscous fluid type heat generating apparatus as incorporated into a vehicle heating system, the rotor element rotates in the heat generating chamber when the drive shaft is driven by the vehicle engine, and the viscous fluid is subjected to a shearing action within the gap between the wall surface of the heat generating chamber and the outer surface of the rotor element to generate heat. The heat thus generated is transmitted to cooling water flowing through the heat receiving chamber by heat exchange, and the cooling water thus heated is supplied through a heating circuit to heat a passenger compartment or the like.
The viscous fluid is withdrawn continuously from the gap through the withdrawing passage into the storing region while the rotor element is in rotation. If the valve means placed in the supply passage is open, the viscous fluid can flow from the storing region into the gap. If the valve means is closed, the viscous fluid cannot flow from the storing region into the gap and, consequently, the viscous fluid is only withdrawn from the gap into the storing region and accordingly, heat generation in the gap is suppressed. Therefore, this viscous fluid type heat generating apparatus can stop heat generation even if the rotation of the drive shaft is not interrupted by operating a solenoid clutch or the like and can prevent the heat generating performance of the viscous fluid from being thermally degraded.
Nevertheless, it is difficult to achieve both more reliable prevention of degradation of the viscous fluid by the thermal and mechanical causes and more reliable prevention of leakage of the viscous fluid from the interior of the apparatus in the prior art viscous fluid type heat generating apparatus of U.S. Pat. No. '778. More specifically, in the prior art viscous fluid type heat generating apparatus, the heat generating chamber has, in addition to the heat-generating gap, the storing region formed to prevent the viscous fluid from being subjected to the shearing action by the rotor element when the fluid is held in the storing region, and the viscous fluid can flow through the storing region and the gap in a circulatory manner. Thus, the shearing of only a particular portion of the viscous fluid does not occur and therefore, the degradation of the heat-generating performance of the viscous fluid due to the thermal and mechanical causes can be avoided.
Nevertheless, in the described viscous fluid type heat generating apparatus of the prior art a relatively large amount of the viscous fluid needs to be stored in the storing region to ensure more reliable prevention of the degradation of the heat-generating performance of the viscous fluid. Thus, if an amount of the viscous fluid stored in the storing region of the heat generating chamber increases, the heat generating chamber is occupied by a large amount of viscous fluid and, accordingly, an amount of compressed gas such as air which remains within the heat generating chamber is reduced. Since the viscous fluid flows between the storing region and the gap, the storing region is directly subjected to the thermal influence from the heat-generating gap. Accordingly, thermal expansion of the large amount of viscous fluid occurs in the gap and the storing region of the heat generating chamber. Hence, the pressure in the heat generating chamber is liable to rise and it is possible that the viscous fluid may leak from the heat generating chamber even if the same chamber is hermetically sealed by shaft sealing devices.